Q&A - PSLE Science

[LionelMessi3175]

Robertpattinsonidle:

Too young for old:

Does anyone know the ans to: explain clearly why it is dangerous to throw a stapler out the window from the 10 floor?(scientific ans pls)

there is alot of GPE which converts to alot of KE. thus the impact will be great. may cause death

I agree with robertpattinsonidie the KE from the stapler will cause pressure and pass the energy to the head of the human and may cause a blood clot because of a strong impact.

[cccleo]

Too young for old:

I agree cccleo. Okay, to simplyfie it, the higher it is above mid point, the more gp it has than ke. Vice versa, the lower it is from mid point, the more ke than gp

That means that the opposite points are with same gpe and ke?

[underthesea]

Please help.


1. Which of the following help an aquatic plant to obtain maximum sunlight?

A: Waxy leaves
B: Clasping roots
Swollen leaf stalks
Air spaces in stems

(1) A and C only
(2) B and D only
(3) A, B and C only
(4) A, C and D only

Answer given is (4). How do swollen leaf stalks and air spaces in stems help to obtain more sunlight?

2. Study the energy conversion below.

Chemical Potential Energy -> Kinetic Energy -> Sound + Head Energy

Which of the following action(s) shows the same energy conversion?

A: Clapping of hands
B: Winding up a toy car
Switching on the ceiling fan
Using a hammer to hit a nail

(1) A and D only
(2) B and C only
(3) A, B and D only
(4) A, B, C and D

Answer given is (1). How come winding up a toy car is not correct? DD thinks the answer should be (3).

[charsen]

underthesea:

Please help.


1. Which of the following help an aquatic plant to obtain maximum sunlight?

A: Waxy leaves
B: Clasping roots
Swollen leaf stalks
Air spaces in stems

(1) A and C only
(2) B and D only
(3) A, B and C only
(4) A, C and D only

Answer given is (4). How do swollen leaf stalks and air spaces in stems help to obtain more sunlight?
>>>>
A: Waxy leaves ---> Prevents water from being collected on the leaves and hence helps the plant from sinking. Plant stays afloat -> helps to obtain sunlight
B: Clasping roots ----> x
Swollen leaf stalks ---> Swollen leaf stalk is filled with air spaces. Helps plant to stay afloat ---> obtain sunlight
Air spaces in stems --> Helps plant to stay afloat ---> obtain sunlight

2. Study the energy conversion below.

Chemical Potential Energy -> Kinetic Energy -> Sound + Head Energy

Which of the following action(s) shows the same energy conversion?

A: Clapping of hands
B: Winding up a toy car
Switching on the ceiling fan
Using a hammer to hit a nail

(1) A and D only
(2) B and C only
(3) A, B and D only
(4) A, B, C and D

Answer given is (1). How come winding up a toy car is not correct? DD thinks the answer should be (3).

>>>> Energy conversion in winding up a toy would result in conversion of Elastic potential energy. Hence Ans 1 is correct

[Robertpattinsonidle]

Robertpattinsonidle:

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why is answer 3? why not 4?

someone pls answer this qsn asap. tmrw i sitting for psle. thanks

[verykiasumummy]

Robertpattinsonidle:

Robertpattinsonidle:

http://i45.tinypic.com/j9566u.jpg\"> http://i46.tinypic.com/2wrm61v.jpg\">

why is answer 3? why not 4?

someone pls answer this qsn asap. tmrw i sitting for psle. thanks

hi,

A) though adil increased higher breathing rate, but it does not mean she used more energy because the increased breathing rate depends on the amount of muscles a person has. since u dun know their mass, u cant deduce that.

B) as similar to above, having same increase in breathing rate doesnt mean using same energy.

hope it helps... good luck for tmr..

[creamyhorror]

Good luck to you kids, and to you mummies/daddies who are cheering for them. You should be in bed already!

[NY1969]

Yes should be in bed now. Need very careful thinking and clear mindset for tomorrow’s battle. A lot of application skills need to be applied.

[Way2GO]

creamyhorror:

charsen:

[quote=\"vaidyanathan padmini\"]I just have a doubt.please help......

Two balls are placed on top of a ramp.ball A has a greater mass than ball B.which ball reaches the ground first?

Thanks in advance

Ball A with greater mass will reach the ground first.
Objects with greater mass will possess higher kinectic energy and hence A will travel faster than B.

In general, if you ignore air friction, objects dropped from the same height fall with the same acceleration, regardless of their mass. This means that objects speed up at the same rate as they fall. A more massive ball will therefore reach the ground at the same time as a lighter ball dropped from the same height. This extends to objects rolling down a slope/ramp, if you ignore friction. So I'd say that both balls reach the ground at the same time.

(The gravitational potential energy (gpe) of the more massive object is higher, and after x seconds of falling it possesses more kinetic energy than the lighter object -- but that doesn't mean it's travelling faster than the lighter object. Kinetic energy is not the same as velocity.)

Let me know if this does not agree with your textbook or teachers


For parents/advanced students: http://www.batesville.k12.in.us/physics/phynet/mechanics/RotMechanics/fall_slide_roll.htm giving the evidence. The summary quote is as follows:[quote]This result says that the linear acceleration of the object down the ramp does not depend on the object's radius or mass, but it does depend on how the mass is distributed. Therefore, all spheres have the same acceleration on the ramp[/quote]Of course, at the primary school level it's unnecessary to go into the details. Just learn that objects with different masses fall through the air and roll down ramps with the same acceleration.[/quote]creamyhorror,
me think u mixed up acceleration with velocity here. d acceleration u refer to in ur post is gravity?
If u meant gravity, it is a given dat d same gravitational force acts on all objects.
If one looks at d question fr a P6 level understanding,
fr a purely conservation of energy point of view, GPE = KE
most P6s will likely reason dat d heavier ball possess greater KE n thus must travel faster or further.
(Since KE is a function of velocity squared, n d heavier ball possesses greater KE, where does d additional KE translate to, if not greater velocity or further distance travelled?)

d answer looks simple on d surface but d explanation requires a much deeper understanding of physics, which is really too much to ask of a P6.
Since it's a ball rolling down a slope, d rotational aspect of each ball must be taken into account. d rotational aspect is what u alluded to in 'distribution of mass'.

It is not a well thought-out question.
Don't u all like to hear d explanation/reasoning fr d teacher who set dis question - for d benefit of students who will come after d current batch?

[Nebbermind]

Way2GO:

creamyhorror,
me think u mixed up acceleration with velocity here. d acceleration u refer to in ur post is gravity?
If u meant gravity, it is a given dat d same gravitational force acts on all objects.
If one looks at d question fr a P6 level understanding,
fr a purely conservation of energy point of view, GPE = KE
most P6s will likely reason dat d heavier ball possess greater KE n thus must travel faster or further.
(Since KE is a function of velocity squared, n d heavier ball possesses greater KE, where does d additional KE translate to, if not greater velocity or further distance travelled?)

d answer looks simple on d surface but d explanation requires a much deeper understanding of physics, which is really too much to ask of a P6.
Since it's a ball rolling down a slope, d rotational aspect of each ball must be taken into account. d rotational aspect is what u alluded to in 'distribution of mass'.

It is not a well thought-out question.
Don't u all like to hear d explanation/reasoning fr d teacher who set dis question - for d benefit of students who will come after d current batch?

W2G

Donch quite get u.

PE = mgh, KE = ½ mv²

Assuming the balls begin with v=0, and h=0 at the end of the slope, then

mgh = ½ mv²
=> gh = ½ v²

Since g and h are constant, v must be the same.